Elite NHS foundation trusts are gearing up to lure private patients from home and abroad as health budgets are squeezed – a decision made possible after health secretary Andrew Lansley said he would abolish the cap limiting the proportion of total income hospitals can earn from the paying sick, research by the Guardian has shown.

With a £20bn black hole opening up in NHS budgets, a group of top performing trusts are seeking to profit from paying patients and use the money to fund public healthcare in Britain. The Guardian contacted the top 10 NHS trusts in terms of private income after the health secretary proposed new freedoms and discovered proposals to build new wings and wards to cater for private patients, set up hospitals abroad and entice medical tourists with airport-to-hospital bed services.

Critics say that because Lansley has abolished targets to reduce waiting times and is encouraging private care, patients will be back to a system where those with cash can jump ahead of those in need. The chief executive of one of the largest NHS hospitals, speaking anonymously, said chasing new markets might also see management spread "too thinly and lose clinical oversight". "Look at Great Ormond Street. They expanded up the road to Haringey Council and the Baby P tragedy happened on their watch," said the chief executive. The hospital in London provided paediatric staff to hospitals where Baby Peter was taken with fatal injuries that are now known to have been deliberately inflicted.

Labour says the policies give "a green light to let market forces run riot through the NHS". Andrew Burnham, the shadow health secretary, said there was "a dangerous combination of lifting the cap on treating private patients and scrapping national waiting time standards," adding: "With no limit on the amount hospitals can earn from seeing private patients, NHS patients can be made to wait. And as waits grow, people will be forced to consider paying for their care. It's the same old Tory NHS choice – wait longer or pay to go private."

But despite concerns that the NHS will wither as private medicine booms, Caroline Shaw, of Manchester's Christie hospital, Europe's largest cancer centre, said it would treble its private income from £10m to £30m within a decade after making a deal last month with the biggest private hospital group in the world, HCA. The deal will see the US-based HCA – which owns six private hospitals in London – pay £14m for a new private cancer centre at Christie. Shaw said staff voiced doubts until they realised half the income went back into the NHS. "We are full of top academics and researchers, so we had to explain we are not losing our values or morals. But we are getting new facilities and it's a 50:50 split of income. I am only half joking when I say we are the new Robin Hoods, taking from the rich to pay for the poor."

Others have gone shopping across the world for rich patients. The Royal Brompton and Harefield, the UK's largest cardio-respiratory centre, devotes an entire section on its website to marketing its "personalised, world-class service" offering patients a city guide and suggesting trips to the "high-end shopping facilities" of nearby Sloane Street and Harrods.

It has emerged that removing the limit on private patients, put in place by Labour, is central to Lansley's reforms. Last week the department of health put out a consultation paper calling for the lifting of the "arbitrary, ill-thought-through cap on [hospitals'] private income ... [to let] the NHS to take proper advantage, for the benefit of this country, of the power of its brand abroad".

Many have taken the health secretary at his word and are targeting the rich in Russia and the Middle East. It is now planning another hospital in oil-rich Abu Dhabi. Moorfields, the eye hospital, opened for business in Dubai and in three years has seen patient numbers jump five-fold to 9,700. Moorfields' total income from private patients tops £13m, with around £4m of that generated in Dubai.

John Pelly, Moorfields's chief executive, said: "Without profits [from our commercial business] our ability to invest in our clinical services would be seriously constrained ... Particularly at a time when the financial constraints facing the NHS are going to be as severe as they are in the next three or four years, it's going to be really important to the NHS that we can take advantage of the abolishing of the cap."

Labour's cap had meant most hospitals were unable to generate more than 2% from private income. The exception is the Royal Marsden, a leading cancer hospital which, thanks to history, has a cap of 31% – and a private income of more than £40m a year. The Marsden, Lansley says, is the "model" in his new-look NHS.

The policy shift has led to smaller trusts thinking big. Papworth Hospital, home to the first successful heart transplant in the UK, will soon be submerged into the new 135-acre Cambridge Biomedical Campus. Some of its operations are so complex – with costs running into £25,000 for 10 hours of surgery – that the NHS can only afford to pay for 80 a year. "I think Andrew Lansley has really thrown down the gauntlet to us. In the next five years we aim to triple private income from 5% today to 15%. There are plans for a completely new private hospital on the campus," said Stephen Bridges, the hospital's chief executive, who has been advised by private healthcare company Spire.

However, academics caution that the rush to the market could lead not to NHS trusts profiting, but to them being undercut by ruthless foreign competitors or losing patients abroad. "What's to stop US healthcare companies coming over here to poach patients. Or GPs sending patients to India for cheap operations? Or English hospitals raiding Scotland for sick people?" said Alan Maynard, professor of health economics at the University of York. "It could be a real mess."

Some are concerned that despite the push the NHS has "missed the boat" when it comes to competing in global private healthcare. Jane Collins, chief executive of Great Ormond Street, which raises £23m from private patients and has just signed a contract in Kuwait to bring seriously ill children to London for treatment, warned: "In terms of UK plc, we are way behind the US, the Germans, Indian companies and Malaysian hospitals."

• This article was amended on 5 August 2010. The original said that Moorfields' private income in Dubai tops £13m. This has been corrected.